Reporting a gift with reservation

Mr G gave up his share of his home to one of his sons, but carried on living there until his death in January of this year. Probate is not required in his estate. Is the correct IHT form to be completed an IHT400 or IHT100 or should both be submitted?

Mr G’s assets therefore include the value he had in his home, With death after 1st January 2022, provided there is no inheritance tax payable, then IHT400 is no longer required, just the other documents.

Thanks for this. Unfortunately the death took place last year.